Porous filter powder



Patented May 23, 1950 2,508,602 roaous m'raa rowmm Alexander Goetz,Pasadena, Calif., asslgnor to Sunshine Mining Company, Yakima, Wash., a

' corporation No Drawing. Application September 9, 1943, Serial No.501,684

3 Claims. (Cl. 210-203) My invention relates to improvements in filtersand filtering materials and methods of producing and using the same. Myinvention more particularly relates to filters and filtering materialsfor filtration of water and other liquids.

My invention still more particularly relates to the practical art offiltration of water, beers, wines and other aqueous liquids employingfiltering equipment comprising a foraminous metal screen, or a screen ofporous ceramic material, carbon, textile fabric, and the like, and alayer deposit of powdery filter material, usually of a siliceous nature,more particularly diatomaceous earth, bentonites and the like, on theupstream side of the screen.

The hereinafter stated principles and examples of the practice of myinvention are not restricted to the use of diatomaceous earth but arealso applicable to other powdery filter materials, including certainbentonites, suitable for use in the filtration of water and otherliquids; and my invention is therefore to be understood as includingsuch other materials as well as diatomaceous earth. However, sincediatomaceous earth is broadly representative of such other filtermaterials while at the same time presenting certain specificcharacteristics rendering its use particularly advantageous in myinvention, for brevity the following descriptions of my invention willbe confined to the use of diatomaceous earth as the filter powder.

It is of the utmost importance to produce a filter powder composed ofdiatomaceous earth, bentonite or the like, which, until intentionallywashed oil the screen, will permanently adhere to the upstream face ofthe screen and form a mechanically coherent filter unit of substantiallyunchanging uniform composition throughout all its parts, and yet withoutappreciable impairment of the original porosity and filtrationproperties of those materials. My invention is directed to theproduction of such filter powder.

Broadly or generally onsidered, my invention comprises so treating aquantity of diatomaceous earth, bentonite or the like with a plasticeither dissolved in a suitable solvent or in a still fluent incompletelypolymerized state, as to cause each individual particle of the material,such as diatomaceous earth. for example, to be uniformly coated with anextremely thin and firmly adher- 2 ing layer of the plastic, avoiding,however, adherence of the plastic-coated particles to each other in thefinished product and with the resulting particles forming, in the mass,a powder of substantially the fineness of the diatomaceous earth beforethe treatment.

The plastic intended by my invention for such treatment of thediatomaceousearth is one which is water-insoluble but susceptible towater in the sense of having the property, when brought in contact withwater, of absorbing water and swelling to larger body volume by suchabsorption. The required quantity of the powder, composed of theplastic-coated individual particles or diatoms of the diatomaceousearth, may be deposited on the upstream face of the screen, beforesubstantial swelling of the plastic coatings occurs, by the sameprocedure employed in the known practical art of water filtration forthe formation of the powder layer or cake of diatomaceous earth.

The plastic coatings on the individual diatoms deposited on the screenvery soon begin to swell. however, as the water fiow is continued,resulting in an interlocking 9f the coated particles with each other andwith the surface irregularities of the screen and the formation of acoherent film of the plastic-coated diatoms which requires anappreciable back pressure of the water for its removal from the screen.Thus, the danger of an unintended or accidental slufiing off of thefilter cake is avoided.

There are a number of plastics having the above stated property of watersusceptibility without being water soluble, and which are suitable forthe above-stated use. As examples, I may employ any one of a number ofcopolymers of vinyl derivatives rich in acetate or any one of a numberof cellulose esters. When employing one of .the copolymers of vinylderivatives, I preferably employ one having approximately %vinyl acetateand 15% vinyl chloride. When employing a cellulose ester, 1 preferablyemploy one of the cellulose acetates or a mixture of cellulose acetates.I.

may, although somewhat less advantageously, employ a vinyl acetate alonefor the water-insolub e but water susceptible plastic.

The required quantity of diatomaceous earth may be subject to any one ofSeveral different 3 procedures for the coating of the individual (11*atoms of that material with a plastic of the nature stated above. Ipreferably employ the following procedure.

A mass of the diatoms is saturated with a liquid which should be eithera solvent for the plastic or compatible with the solvent to be usedtainer. The mass of diatoms in that saturation,

state is a non-fluent mass in the form of a soft cake. The plastic, inthe required quantity, and either in partially or completely polymerizedform.

is dissolved separately in dichlorethane or in some other selectedsolvent compatible with dichlorethane, such asv methyl ordimethylbenzene, or a cyclic ketone or mixtures of those or similarsolvents. The previously saturated mass of diatoms and the solution ofthe plastic are then intimately mixed mechanically, resulting in anintimate combination of the diatoms and the plustic, with the latter asa film-like coating over each diatom. This coating is a thin surfacefilm without substantial penetration into the pores of the diatoms dueto the saturation state of that material previously accomplished.

The material (the mass of diatoms with the plastic in solution as a thinsurface film on each diatom) is then subjected to mild heat or a vacuumdrying procedure to drive off the solvent. Thus there is produced, asthe finished product, a fine powder mass of diatoms each coated with anexceedingly thin film of the plastic, and with that powder ready for itsbeforementioned use as a filter powder firmly adhering to the screen ofthe filtering unit, by reason of the swelling of the plastic coatingwhen in contact with the water undergoing filtration.

It may be further noted, however, that the plastic-coated diatoms arenot readily wetted by the water until some time has elapsed after theirbeing placed therein and hence will not at first sink below the surfaceof the water flowing to the screen, as is necessary for their initialdeposition on the upstream face of the screen. That delay in theformation of the powdery layer or cake of the plastic-coated diatoms onthe screen may be avoided, however, by treating the mass ofplastic-coated diatoms with any of the numerous well-known wettingagents, such as certain sulfonated hydrocarbon derivatives, of which thegroup of wetting agents known under the trade name "Aquaphor. istypical.

As hereinbefore stated, the layer or cake of diatomaceous filter powderfirmly adheres to the Y Such coagulating agent may be any one of thehydroxides or sulfates of Al and Fe ions, of which alum and ironhydroxide are typical examples. For the incorporation of the coagulantin the plastic coating which is to be formed on each diatom, a smallquantity of the selected coagulant, in minutely fine subdivision, may bemechanically mixed with the solution of the plastic before the latter ismixed with the mass of diatoms, the procedure in the formation of thecoating being otherwise as before described, and the result being anincorporation of the coagulant, such as finely divided alum, forexample, into the plastic coating on each diatom.

It is also highly desirable in some cases, particularly in thefiltration of water for drinking purposes, to have the filter functionnot only in the filtration but also in the sterilization of the water.To that end, my invention further comprises the incorporation of awater-insoluble germicidal composition as a colloidal suspension in theplastic prior to coating the diatoms with the plastic. To that end, mypresent invention preferably employs a germicidal composite powder ofcolloidal carbon and silver with the latter in an adsorbed andactivating oxygenated state on the carbon as described and claimed in mycopending application Serial No. 469,578, filed December 19, 1942, whichhas become abandoned. It has been found advantageous in improving thegermicidal action of the just mentioned germicidal compositions ofcolloidal carbon and silver to incorporate together with suchcomposition a basic heavy metal oxide, such as zinc oxide. titaniumoxide and the like, in'a state of extremely fine subdivisions into theplastic. The incorporation of the germicidal carbon-silver colloid andthe finely divided metal oxide into the plastic coating on the diatomsmay be attained by the same procedure mentioned above for incorporationof the coagulants into the plastic.

In the practical application of such germicid' ally active powders forwater sanitation, the method of powder filtration as commonly practicedinvolves an inherent handicap caused by the possibility of an infectionor bacterial contamination of the down-stream parts of the filter by theinitial water flow which has passed through the screen before anadequate filter cake of the plastic coated diatoms containing theabovementioned germicidal composition in the plastic has formed on theupstream face of the screen, and also by the residual bacterialcontamination on the downstream side of the filter unit. That danger cansuccessfully be avoided, however, in my invention byjthe addition of awater-soluble disinfecting agent to the filter powder in a quantitysufllcient for accomplishing the iiiitial disinfection of the involvedparts of the downstream side of the filter. Because ofits watersolubility, this disinfecting agent is leached out of the filter powderimmediately upon contact of that powder with the water and thus thedisinfecting agent is carried initially through all parts of the filter.

water-insoluble germicidal composition in the plastic coatings on thediatoms. The abovementioned colloidal carbon-silver germicidalcomposition preferably employed in the plastic coatings on the diatomscomprises a surface com-' pound of silver and oxygen on the carbon, andit is well known that silver-oxygen compounds act catalytically uponhydrogen peroxide. Also, experiments have shown that a very much smallerquantity of hydrogen peroxide can be used in the presence of such asilver-oxygen compound in order to impart the required germicidalproperties to the water than would be required without the presence ofthe silver-oxygen compound.

Another advantage of the choice of hydrogen peroxide for theabove-mentioned specific purpose is its relatively short life ashydrogen peroxide in water. Whereas that is a handicap for general useof hydrogen peroxide in water sanitation, it is an advantage for itsabove-stated specific use which requires its disinfecting action only inthe very initial stages of the filtration before the layer or cake ofthe diatoms having the water-insoluble germicidal composition in theirplastic coatings has had time to completely form on the screen. Afterthat cake has formed on the upstream face of the screen, the hydrogenperoxide is no longer needed and should disappear as soon as possible inorder to avoid imparting an unpleasant taste to the filtrate.

Because of the very nature of the intended application of thewater-soluble disinfectant,

that is, as an admixture to the dry filtration powder prior to use, itis necessary, however, that the hydrogen peroxide be added in the formof a solid powder to the filter powder. It is, therefore, evident thathydrogen peroxide as such cannot be used and that, instead, a solidmaterial yielding-hydrogen peroxide upon contact with water should beused. Urea peroxide is such a water-soluble solid substance yielding theperoxide upon contact with water; and my invention comprises its use forthe above-stated purpose. For such use the urea peroxide is pulverizedand mechanically mixed with the dry powder of plastic-coated diatoms.

I claim:

1. A porous filter powder comprising diatoms and a plastic coating oneach individual diatom, said plastic of said coating being one of thecopolymers of vinyl derivatives having approxi- 6 mately vinyl acetateand approximately 15% vinyl chloride in its composition and having theproperty of absorbing water and swelling to increased volume of saidcoating upon said absorption.

2. A porou filter powder as recited in claim 1 and a germicidalcomposition composed of colloidal carbon and silver in an oxygenatedstate carried on said carbon, said germicidal composition being embeddedin said plastic coating.

3.' A substantially dry filter powder comprising a porous mass of finegranular particles of a water-insoluble solid material adapted for thefiltration of aqueous liquids. each particle of said mass having acoating of a water-insoluble plastic having the property of absorbingwater and swelling to substantially larger body volume by suchabsorption, said plastic being one of the copolymers of vinylderivatives rich in acetate.

ALEXANDER GOETZ.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 589,638 Busch et a1. Sept. 7,1897 1,078,918 Gruter Nov. 18, 1913 1,473,331 Bechhold Nov. 6, 19231,557,235 Bechhold Oct. 13, 1925 1,576,440 Martin Mar. 9, 1926 1,579,171Zoul Mar. 30, 1926 1,777,546 Blumenberg Oct. 7, 1930 1,935,577 Reid Nov.14, 1933 1,981,877 Pierce Nov. 27, 1934 2,040,818 Badollet May 19, 19362,066,271 Irwin Dec. 29, 1936 2,106,318 Elliott et a1. Jan. 25, 19382,167,225 Van Eweyk July 25, 1939 2,195,196 Wassenegger Mar. 26, 19402,198,378 Ellis Apr. 23, 1940 2,219,581 I Schmidt Oct. 29, 19402,232,153 Vohrer -Feb. 18,1941 2,243,826 Nielsen et al. May 27, 19412,315,410 Simons et al Mar. 30, 1943 2,327,250 Cruickshank Aug. 17, 19432,328,361 Sanders Aug. 31, 1943 2,340,110 DAlelio Jan. 25, 19442,340,111 DAlelio Jan. 25, 1944 2,355,822 Rugeley Aug. 15, 1944 FOREIGNPATENTS Number Country Date 427,199 Great Britain Apr. 17, 1935 OTHERREFERENCES tion, page 1231, 1943.

1. A POROUS FILTER POWDER COMPRISING DIATOMS AND A PLASTIC COATING ONEACH INDIVIDUAL DIATOM, SAID PLASTIC OF SAID COATING BEING ONE OF THECOPOLYMERS OF VINYL DERIVATIVES HAVING APPROXIMATELY 85% VINYL ACETATEAND APPROXMATELY 15% VINYL CHLORIDE IN ITS COMPOSITION AND HAVING THEPROPERTY OF ABSORBING WATER AND SWELLING TO INCREASED VOLUME OF SAIDCOATING UPON SAID ABSORPTION.